PAMM
A measuring system for the determination of the intrinsic permeability of highly porous materials is presented. The evaluation of the measurements is conducted on the basis of the Theory of Porous Media (TPM). By adjusting the calculation to the measurement results achieved with polyethylenglycol (PEG) 300 and open‐cell aluminium foam, the intrinsic permeability of the metal foam is determined. (©...
Flow control refers to the ability to alter flows with the aim of achieving a desired effect: examples include drag reduction, noise attenuation, improved mixing or increased combustion efficiency among many other industrial applications. The reduction and control of the viscous drag force exerted on bodies moving in a fluid is of great technical interest. Several active and passive methods to achieve...
This work presents a numerical study of the flow of molten metal in the shot sleeve of horizontal high‐pressure die casting machine during the injection process. The analysis of the wave of the molten metal created by plunger motion can be of help in reducing porosity in manufactured parts caused by air entrapment. The used numerical model, which considers the problem as two‐dimensional, is based...
Viele Werkstoffe, wie Kunststoffe oder Elastomere, zeigen viskoelastisches Materialverhalten. Der Ansatz zur Modellierung dieses Materialverhaltens kann mit Hilfe sogenannter rheologischer Ersatzmodelle veranschaulicht werden, wobei ein wichtiger Bestandteil das Maxwell‐Element ist. Da die genannten Werkstoffe zum Teil großen Deformationen unterzogen werden, ist eine Modellierung des gesamten Materialverhaltens...
Cyclic loading of single‐ and polycrystals gives rise to complex structures and patterns on the material's microscale, which highly affect the macroscopic stress‐strain response. The formation of microstructures in finite‐strain crystal plasticity has been reasoned to stem from the non‐quasiconvexity of the underlying energetic potentials. As a consequence of such a lack of convexity, the material...
In this paper the dynamical theory of elasticity for solids with double porosity is presented. The single‐layer and double‐layer potentials are constructed and basic properties are established. The uniqueness theorems of the internal and external boundary value problems (BVPs) of steady vibrations are proved. The existence theorems of classical solution of the external BVPs by means of the boundary...
Structural dynamic properties like stiffness and damping are strongly influenced by contact phenomena in jointed structures. Therefore numerical and experimental investigations are presented, in order to understand and predict the behaviour of such mechanical devices. (© 2010 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nonlinear behavior of piezoceramics is a well‐known phenomenon. For large stresses and/or strong electric fields it is described by various hysteresis curves. Quasi‐static experiments exhibited hysteresis relations between excitation voltage and strain as well as between excitation voltage and electric displacement. This behavior can be modeled by using the classical Preisach model. On the other hand,...
Metal‐ceramic composites produced by melt infiltration of the ceramic preform were studied. The ceramic preform of these materials is manufactured through freeze‐casting process and the microstructure can be presented as distribution of the lamellar domains. Micromechanical models were used for the calculation of the effective elastic properties of the domains. The minimum compliance problem was solved...
We consider free oscillations of a double pendulum, where one of the pendula is modelled as a very stiff spring. Contrary to a single spring pendulum numerical simulations show an unexpected large influence of the fast longitudinal oscillations on the slow pendulum oscillations even for extremely large values of the stiffness. The transition from the regular motion, which is governed by the dynamics...
The PUR‐fiber‐spray molding technology is a manufacturing process which produces polyurethane‐based (PUR) composites by spraying the matrix together with reinforcing fibers in a tool form or on a substrate. Thereby chopped fibers are laterally (sidewise) injected in the polyurethane‐air spray cone for wetting before the entire composite is spread on the substrate, where it starts curing. To investigate...
Rotating friction disks are utilized in many drivetrain components such as dry clutches and their actuator systems. Even the simplest pin‐on‐disk or disk‐on‐disk mechanical systems with Coulomb friction reveal a rich dynamical behavior with different types of motions.
Examining the radial dynamics of minimal friction disk models, it is a prevalent assumption to have pure sliding frictional contacts...
The present study is concerned with an analysis of load‐frequency interaction effects in the dynamic buckling response of soft‐core sandwich plates and shells. Based on a higher‐order geometrically non‐linear sandwich shell theory in conjunction with an extended Galerkin procedure, a mathematical model together with analytical solution for simply supported sandwich plates and shells with with rectangular...
Motivated by the study of self‐cleaning surfaces, the interaction between a spherical solid particle and a water droplet is studied on the microsale level, in terms of the balance forces and the surface properties. To define the forces acting on the solid‐liquid interface, the meniscus depression is computed from the Young‐Laplace equation, using a non‐linear finite element formulation. The equilibrium...
Bones are strong and lightweight structures, which mainly consist of extracellular bone matrix. The bone remodelling is a process of resorption followed by replacement of the bone matrix with small changes in shape, which allow the bones to adapt according to the local loading situation.
In the context of the Theory of Porous Media (TPM), a consistent model of bone tissue is introduced, which is able...
Micro‐computed tomography (µCT) is a widely used imaging technique. Tomography has been used to study the distribution of magnetic nanoparticles within cancerous tissue after minimal‐invasive cancer treatments such as magnetic drug targeting and magnetic hyperthermia. But not only the distribution is a relevant factor for the sucess of these therapeutic aproaches. The concentration of the magnetic...
The aim of the present study is to investigate the strength and damping properties of cellular articular cartilage replacement material. For this purpose, a viscoelastic‐diffusion model for the acellular water‐saturated condensed collagen gel type I is proposed and validated experimentally. Moreover, a remodelling law for the cell seeded collagen gel is introduced. For an experimental study of the...
Material properties in general and layer‐specific stiffness in particular are critical factors to predict the initiation and growth of aneurysms. Previous experimental studies show vastly differing material stiffness and metabolic activity in the media and the adventitia. In this paper a phenomenological model using FEM is applied in order to predict the adaptive response of the arterial wall in different...
In this contribution, an efficient computational approach for modeling the physiological contact conditions in synovial joints is presented. A detailed three‐dimensional finite element model of the hip joint is generated based on CT‐data. The synovial gap between the porous cartilage layers is discretized with shell‐like liquid interface elements. In these elements, the Stokes flow equations are solved...
Elasticity imaging or elastography is a powerful technique in medicinal imaging for visualizing the stiffness distribution in soft tissue in vivo. It is motivated by the observation that the stiffness in soft tissue is affected by pathologies in many cases. More precisely, diseased tissue tends to be stiffer than the healthy surrounding tissue. The two steps involved in elasticity imaging are: first...